The amniotic sac is a pair of membranes that enclose a developing embryo as it develops to a fetus. The amniotic sac includes an inner membrane called the amnion that contains the amniotic fluid and the fetus, and an outer membrane called the chorion that contains the amnion and a portion of the placenta. Amniotomy is the artificial rupture of membranes (AROM) that is usefully employed to induce and/or accelerate labor.
U.S. Pat. No. 4,662,376 provides an amniotomy instrument that includes a curved tube having a handle and a suction piston movably mounted within the tube. The tube terminates in a bell-shaped structure at a distal end, and includes piercing pins mounted within the tube. The piercing pins are positioned such that they cannot contact the fetus even as the amniotic sac is drawn into the tube. The instrument is configured for two-hand operation by an attending physician, where the piston is retracted within the tube, and a portion of the amniotic sac is drawn into the distal end of the tube to be pierced by the piercing pins.
U.S. Pat. No. 5,968,055 provides another amniotomy instrument. The instrument includes a curved elongated shaft having a distal end, where the distal end includes a rounded structure curved over a sharp, pointed hook. During use, the attending physician positions an index finger along the rounded structure to guide the sharp pointed hook to the amniotic sac. When in position, the hook is engaged with the amniotic sac to perforate the membranes.
Although generally effective and useful, the known AROM devices are not suited for access through a minimally dilated, relatively closed cervix. Improvements to the devices employed to perforate the amniotic sac would be welcomed by obstetric physicians and their patients.